The term plasma antenna has been applied to a wide variety of antenna applications that incorporate the use of an ionized medium. In the vast majority of approaches, the plasma, or ionized volume, simply replaces a solid conductor. A highly ionized plasma is essentially a good conductor, and therefore plasmas can serve as transmission line elements for guiding waves, or antenna surfaces for radiation. The concept is not new. A patent entitled “Aerial Conductor for Wireless Signaling and Other Purposes” was already granted to J. Hettinger in 1919 (U.S. Pat. No. 1,309,031). A more recent prior art is disclosed in the U.S. Pat. No. 6,621,459 B2, “Plasma Controlled Antenna”, by Webb et al, describing a plasma controlled millimeter wave or microwave antenna where a plasma of electrons and holes is photo-injected into a photoconducting wafer, having a reflecting surface behind the wafer allowing the antenna to be generated at low light intensities and a 180 degree phase shift (modulo 360 degrees). This patent describes a way to reconfigure the antenna but it remains electrically visible due to the constant presence of the conducting reflector in the beam path. Another approach is described in the U.S. Pat. No. 5,982,334, “Antenna with Plasma Grating”, by Manasson et al. Nov. 9, 1999, where scanning antennas with plasma gratings is described. The latter includes a semiconductor slab and an electrode set or an illuminating system for injecting plasma grating, enabling beam steering. This system is not electrically invisible when not operating, and is confined to one dimension in steering.
There is therefore a need for an optically driven, reconfigurable, plasma antenna that can be “turned off” when inactive, to render it electrically invisible for the purpose of reducing its scattering or reflecting signature and eliminating its coupling and interference with other nearby antennas.